In bubble jet print heads a plurality of very small resistive heater elements are formed (e.g. by photofabrication) on a support (e.g. a silicon or glass chip having a heat control coating). Metal electrodes are formed on the chip to couple the heating elements for selective energization and a protective coating is provided over heat elements and electrodes. A top member is provided over at least the portion of the chip having the heater elements and ink is supplied to the region between the cap and heater elements, preferably by capillary feed from a supply reservoir. When a heater element is selectively energized, the contiguous ink is converted to steam rapidly and the resultant shock wave ejects ink from an orifice related to that heater element.
As the development of bubble jet devices has progressed, two general categories of drop ejection approach have evolved: (i) ejecting drons in a direction generally parallel to the surfaces of the heater elements and their electrical circuitry and (ii) ejecting drons in a direction generally normal to the heater element surfaces. U.S. Pat. No. 4,330,787 describes several advantages of the latter category of devices, herein termed "normal" drop ejector devices.
In prior art bubble jet print heads a variety of ink channel structures have been provided between the top cap member and the chip for purposes of fluid isolation between drop ejection zones, enhancing capillary ink transport and providing structural support between the drop ejecting chip and top member. The channel structures have been fabricated in a variety of ways, e.g. electroforming baffle elements as portions of the orifice plate/top member (see U.S. Pat. No. 4,528,577), micro-cutting grooves into a glass drop-ejection chip (see U.S. Pat. No. 4,330,787) and photofabricating photoresist or photopolymer channel patterns (see U.S. Pat. Nos. 4,417,251; 4,412,251 and 4,746,935).
In all such print head devices a major concern with design must be to assure that the devices can be fabricated with precise alignments between the heater elements, the channel structures and the drop ejection orifices. The photofabrication of channel structures provides a good approach for heater/channel alignment. However, orifice plates are usually separate parts from the heater elements and photofabrication alignment of orifices vis a vis heater element has not been available. This is particularly so with respect to the "normal" drop ejector devices, and in that kind of device orifice/heater element alignment is especially critical. In addition, electroplating stresses tend to shrink or elongate electroformed orifice plates vis a vis a nominal dimension. This further complicates the attainment of good heater/orifice alignment when electroformed orifice plates are used.